Would it be possible to transfer items from Blue Burst to PSO PC V2 or PSO PC to Gamecube? I am aware of the cross platform feature but not sure if it's possible to transfer by dropping items or trade window. Thanks.

Blue Burst can't even play on Sylverant, so you can't get any items to transfer. Transferring items between DC/PC and GC will often break the items you try to transfer, as the items are coded differently between versions and have different limitations in their stats. For example, weapons in GC can have percentages up to 100, while PC limits percentages to 60. If you transfer a GC weapon with 80% to PC, PC will delete the percentage, because it thinks the weapon is hacked.